Power management in an eye-tracking system

ABSTRACT

An imaging device adapted to provide eye-tracking data by imaging at least one eye of a viewer, wherein: the imaging device is switchable between at least an active mode and a ready mode; the imaging device is configured, in the active mode, to use active eye illumination, which enables tracking of a corneal reflection, and to provide eye tracking data which include eye position and eye orientation; and the imaging device is configured, in the ready mode, to reduce an illumination intensity from a value the illumination intensity has in the active mode.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/831,511 filed on Dec. 5, 2017, which is a continuation of U.S.application Ser. No. 15/233,761 filed on Aug. 10, 2016, now U.S. Pat.No. 9,866,754, which is a continuation of U.S. application Ser. No.14/608,006 filed on Jan. 28, 2015, now U.S. Pat. No. 9,442,566, which isa continuation of U.S. application Ser. No. 13/283,224 filed on Oct. 27,2011, now U.S. Pat. No. 8,976,110, all of which are hereby expresslyincorporated by reference into the present application.

TECHNICAL FIELD OF THE INVENTION

The invention disclosed herein generally relates to eye tracking(determination of eye position, gaze point or gaze angle) for providinginput data to a computer system. In particular, the invention providesan energy-efficient implementation of eye tracking assisted by anartificial light source adapted to determine the gaze point of an eyewatching a visual display forming part of a portable or stationarypersonal computer system, a TV, a heads-up display in a vehicle, anear-eye display or a display in a communication device with imaging andcomputing capabilities, such as a mobile telephone.

BACKGROUND OF THE INVENTION

Monitoring or tracking eye movements and detecting a person's gaze pointcan be used in many different contexts. Eye tracking data can be animportant information source in analyzing the behavior or consciousnessof the person. It can be used both for evaluating the object at whichthe person is looking and for evaluating the respective person. Thediverse uses of gaze point detection include studies on the usability ofsoftware and different types of interfaces; evaluation of web pages,advertising and advertisements; provision of means for educating pilotsin simulator environments and for training surveillance personnel insecurity-critical roles; and research in psychology, behavioral sciencesand human perception. A field which has attracted an increasing interestin recent years is the evaluation of advertising and other marketingchannels.

Eye-tracking techniques can also be used in a human-machine interface(HMI): a user can control a computer by just looking at it. Such eyecontrol can be applied as sole interaction technique or combined withkeyboard, mouse, physical buttons and voice. Eye control is used incommunication devices for disabled persons and in various industrial andmedical applications.

While eye-tracking systems are utilized in a growing range ofapplications aimed at professionals, they are rarely included asstandard peripherals in or as integral parts of new laptops, desktops,smart phones and other personal computer systems. In the case ofbattery-powered systems, concerns that eye-tracking functionalitiesmight impair an otherwise optimized energy management may be one reasonfor this absence.

US 2005/199783 A1 describes a technique for switching a generic devicebetween a power-up state, a sleep state and a power-off state on thebasis of eye detection data relating to a user. Only the presence orabsence of an eye is of concern, not the gaze angle. A detected presenceof an eye causes switching from the sleep state to the power-up state,while a detected absence causes switching down from the power-up stateto the sleep state, and then to the power-off state of the device. Whilethis document describes how an eye detection result, namely eyepresence, can be used to improve the energy performance of the genericdevice, it does not address the power management problem in the eyedetection equipment itself. Nor does it propose any solution that istailored to, and benefits from, the particularities associated with eyedetection activity.

Similarly, U.S. Pat. No. 5,835,083 A and WO 2008/056274 A1 discuss howgaze-point measurements can be used to control a power state of a visualdisplay, so that power consumption is reduced when a user's eyes andhence a user's attention are not directed to the device. They also donot address power management in the eye tracker itself.

SUMMARY OF THE INVENTION

In view of the above concerns, it is an object of the present inventionto propose a personal computer system with improved power managementfunctionalities in respect of eye-tracking equipment included therein.It is a particular object to improve power management in a system ofthis type while preserving low latency in respect of user interactionsat all instants when the device is operating. Yet another object is toprovide an eye-tracking system that can be integrated in a personalcomputer system (e.g., desktop or laptop computer, tablet computer,notebook, net book, TV, smart phone, personal digital assistant, digitalcamera, heads-up display, near-eye display) without burdening the energyperformance of the computer system.

At least one of these objects is achieved by a method, computer programproduct, and personal computer system, as set forth in the independentclaims. The dependent claims define embodiments of the invention.

A personal computer system includes a visual display, an imaging devicefor providing eye-tracking data by imaging a portion of the face(preferably including at least one eye) of a viewer of the visualdisplay, and further one or more input means for accepting eye-trackingcontrol data and other input data. The imaging device may include acamera and an optional light source for illuminating an eye in anon-axis or off-axis fashion, or for producing at least one cornealreflection (or glint, or first Purkinje reflection) to facilitate eyetracking. Such illumination which the imaging device provides inaddition to natural or background light sources will be referred to asactive illumination. The other input data may include pointing devicesignals, keyboard characters, keyboard combinations, visual data otherthan eye-tracking data, proximity sensing, data acquired by an acoustictransducer and the like.

According to a first aspect of the invention, the imaging device isoperable in at least an active mode, a ready mode and an idle mode. Inthe active mode, the imaging device is fully operable as regardsaccuracy, detection range and other performance parameters that mayinfluence the momentary power consumption of the device. The ready modeand the idle mode represent power-saving alternatives to the activemode, which differ at least with respect to their respective wake-uptimes. More precisely, the wake-up time required to switch from readymode into active mode is shorter than the wake-up time required toswitch from idle mode into active mode.

The invention achieves at least one of its objects since the proposedenergy management technique takes into account the fact thateye-tracking algorithms generally contain recursive filtering (e.g.,Kalman filtering), wherein the accuracy is improved gradually with thenumber of iterations, or are dependent on previous measurements,intermediate data or partially processed data to be used as initialguesses for subsequent tracking. An eye-tracking algorithm of this typedoes not provide accurate and complete measurement data from the momentit is cold-started, but only after a wake-up time period has elapsed.Hence, in the prior art, the requirements of low energy consumption andresponsiveness (low user latency) are clearly conflicting. The inventionalleviates this difficulty by proposing a ready mode, in which theeye-tracking equipment operates at lower but non-zero power, so that aportion of the previous measurements, intermediate data or partiallyprocessed data remain updated and available to support and facilitatesubsequent measurements when the equipment switches back into its activemode.

The active, ready and idle mode may differ regarding the state of(components of) the imaging device only, but may also differ withrespect to operational parameters of other components in the personalcomputer system. For instance, the fact that the imaging device entersits off mode may trigger turn-off of a backlight in the visual display.

The imaging device may consist of a camera only, preferably a digitalcamera, but may also include further components, such as a light sourcefor assisting the camera, e.g., by emitting non-visible light pulsespreferably in the infrared or near-infrared range. Within the imagingdevice, therefore, either the camera only, the light source only or acombination of these and possible further components may behavedifferently in the active, ready and idle mode, respectively. As usedherein, the term imaging device is not restricted to optical cameras,but is also intended to cover acoustic (e.g., ultrasound),electromagnetic (e.g., radar) sensors. The term also extends beyondthose sensors which produce images that are perceived as such by a humanviewer, thereby covering sensors formed as arrangements of asingle-digit number of pixels, sensors including highly distortingpre-lenses intended to favor optical accuracy in regions of interestover other regions etc. Furthermore, the imaging device may be directedtowards one or more of the viewer's eyes only but may as well image alarger portion of the face so as to determine a relative head pose, andthe gaze may be determined based on the position of at least one eye inthe face.

The active and ready modes may differ with regard to the data theimaging device provides. In the active mode, both eye position and eyeorientation may be provided. (To make this statement precise, theimaging device may output processed data representing eye position andeye orientation or, if it lacks appropriate processing capabilities ofits own, the imaging device may output sufficient raw image data that aprocessor is able to determine eye position and eye orientation. Thereceiver of the output data may be a processor responsible for executinga graphical user interface forming part of application software, adesktop environment or the like.) In the ready mode, however, either ofthese may be omitted to save resources, preferably eye orientation sothat only eye position is provided. The eye position tracking mayproceed throughout the ready mode, though preferably at a lower framerate than in the active mode, so that up-to-date information on the eyeposition is readily at hand at the moment the imaging device switchesback into active mode. This reduces the wake-up time significantly,while the energy consumption in ready mode may be limited significantly.

Alternatively, the active and ready modes may differ with respect to thenumber of distinct tracked eye features (e.g., pupil location, cornealreflections) on which the imaging device bases the eye-tracking data. Inactive mode, the eye tracking may be based on two or more features. Forexample, the eye-tracking processing may be based on reflections of noless than two distinct light sources (including the case where thereflections are captured within different camera frames), whereas inready mode, the eye tracking may be based on a single distinctreflection, such as may be obtained using one single light source(including the case where a reflection of this light source is imaged atmultiple points in time within different frames), that is, theeye-tracking processing is able to complete based on data from a singlereflection. It is recalled that gaze tracking according to thepupil-centre-corneal-reflection (PCCR) approach requires as input thelocations of a pupil and a corneal reflection that are simultaneous ornear-simultaneous (see, e.g., the paper General Theory of Remote GazeEstimation Using the Pupil Center and Corneal Reflections by E. D.Guestrin and M. Eizenmann, IEEE Transactions on Biomedical Engineering,vol. 53, no. 6, pp. 1124-1133 (June 2006), included herein byreference). The camera-to-eye distance may be a further input datasource in PCCR gaze tracking. It is described in U.S. Pat. No. 7,572,008how this distance can be estimated on the basis of two distinct cornealreflections. Accordingly, the eye tracker may refrain from updating thelatest estimate of the camera-to-eye distance when in the ready mode butmay do so intermittently in the active mode.

Further advantageous examples indicating how the active and ready modescan be configured in detail are noted in Table 1.

TABLE 1 Mode configurations Active mode Ready mode The imaging devicetracks a pupil The imaging device tracks a pupil location and at leastone corneal location. reflection. The imaging device applies active Theimaging device does not apply illumination, which enables trackingactive illumination. of a corneal reflection. One light source and onecamera are Two light sources and one camera active. are active. Onelight source and one camera are active. One light source and two camerasare active. One camera is active. One light source and one camera areactive. The imaging device operates at full The resolution of theimaging device is resolution. reduced by binning pixel groups, e.g., by2 × 2 (ratio 4:1), 4 × 4 (ratio 16:1), 1 × 2 (ratio 2:1), 2 × 1 (ratio2:1), wherein multiple pixels are read out as one. Preferably, sincebinning increases the sensitivity of the imaging device, an associatedlight source is operated at lower intensity or is turned off completely.Additionally, the exposure time of the imaging device may be increased,thereby further increasing sensitivity at the cost of some accuracy. Theimaging device operates at a The imaging device operates at a relativelylower binning ratio, e.g., 2:1. relatively higher binning ratio, e.g.,16:1. The imaging device measures or The imaging device measures orestimates an eye position in world estimates an eye position in image-coordinates (e.g., n-dimensional plane coordinates (e.g., (n-1)-coordinates or 3-dimensional dimensional coordinates or 2- coordinates).dimensional coordinates).

It is pointed out that the scope of the invention includes combinationsof the above pairs as well. Likewise, binning may refer to analoguebinning, such as by reading out pixel charges in a group-wise fashion,so that luminous energy received at a plurality of pixels contribute toone value. It may also refer to digital binning in the sensor, which mayform part of a pre-processing step involving adding or combiningread-out data pixel values in processing hardware.

Moreover, in a system where plural cameras and/or plural light sourcesare provided, the ready mode may involve using a smaller number of thesedevices. Since estimations based on a smaller data set may have greaterstatistical variance, this mode may lead to slower and less accurate eyetracking data but may still provide sufficient information tosignificantly shorten the time for switching into active mode andcollecting relevant eye-tracking data in comparison with a cold startfrom idle mode.

The input means in the personal computer system may consist of adedicated input means on the one hand and general-purpose input means onthe other. It may also consist only of either of these, as mentioned inthe next paragraph. The dedicated input means are used to inputeye-tracking control data only, whereas the general input means acceptall other input data than eye-tracking data, that is eye-trackingcontrol data and other input data. Because the dedicated input means isused only for eye-tracking control data, the operating system mayallocate to it abilities to activate the eye tracker with lower delaythan the general-purpose input means would achieve. The dedicated inputmeans may be configured as a camera for detecting predefined facegestures, predefined body gestures or a microphone for detecting apredefined voice pattern. Advantageously, the camera used for thispurpose is identical to the at least one imaging device that suppliesthe eye-tracking data. The dedicated input means may further be embodiedas a hardware or software button, an IR sensor, a motion sensor, aproximity sensor, a touch-sensitive layer of a visual display or aportion thereof. In the latter case, one touch-sensitive display maycomprise both an area acting as a dedicated input means and an areaacting as a general-purpose input means.

Said eye-tracking control data entered via the dedicated input means maybe an activation click, that is, a mouse-click-type signal supplementinga gaze point on the visual display to achieve a similar interface asthat offered by a conventional pointing device, although this need notbe organized on the basis of the pointer location as such conventionalsystems generally are. A completely hands-free HMI, in which all inputdata are entered either in the form of eye-tracking data or eye-controldata, is envisioned. Additional input means in such hands-free HMI mayinclude acoustic, haptic or optic transducers and the like but is devoidof devices adapted to be mechanically manipulated using fingers, handsor other body parts.

Said eye-tracking control data may also be used to switch theeye-tracking functionalities between an enabled state and a disabledstate, which may be particularly attractive for users conscious aboutpersonal integrity. As one possible option, the dedicated control meansmay be configured to force the imaging device into idle mode.

Alternatively, the dedicated input means may trigger an interrupt bywhich the imaging device is forced into active mode. The triggering maybe achieved by functionally connecting the dedicated input means to aninterrupt means (e.g., an interrupt pin) provided on the imaging deviceor on a processor associated therewith. Preferably, the dedicated inputmeans is functionally disconnected from the interrupt means in theactive mode, so as not to perturb the work of the imaging device duringactive mode, wherein the computational load is relatively higher than inother modes. By using an interrupt in this manner, the total latencyassociated with a switching into the active mode is reduced incomparison with the case of triggering the switching by means of thegeneral-purpose input means, which typically have an inherent latency.Most of today's low-grade and middle-grade keyboards, mice, touchscreens and other general-purpose I/O devices, of the type which a usermay be expected to connect to a personal computer system in theirpossession, operate by line scanning followed by interrupt generation.Such an interrupt is generated indirectly, not by the user's actuationbut by the scanning result. This principle of operation incurs a delay,which is typically negligible in the intended use of the I/O device(e.g., typing) and therefore rarely improved on by the manufacturer, butwhich makes a general-purpose I/O device poorly fit to inputeye-tracking control data. Indeed, the latency contributed by the I/Odevice adds to the wake-up time of the imaging device itself, so thatthe total latency may become larger than is acceptable in a givenapplication. This embodiment of the invention resolves the problem bytriggering an interrupt directly.

In a further embodiment, the imaging device is powered separately, suchas via an autonomously controllable electric switch connecting it to adrive power necessary for its operation. With this setup, the idle modemay consist in a complete power-off state of the imaging device. Hence,advantageously, the dedicated input means forces the imaging device intoidle mode by disconnecting it from said drive power.

The active, ready and idle mode may differ with respect to an operatingfrequency of the imaging device. Generally, the operating frequency mayrefer to any frequency characterizing a component within the imagingdevice, to the extent that the frequency influences the momentary powerconsumption. In particular, the operating frequency may be the samplingfrequency (or frame rate) of a camera within the imaging means. It mayalso refer to a light-pulse frequency of a pulsed light source used inconnection with a camera of this type, wherein each light pulse issynchronized with a sampling instant of the camera. In particular, theactive and the ready mode may differ in terms of the operatingfrequency, wherein the ready mode is associated with a lower, non-zerofrequency which maintains eye-tracking at a less accurate level. Such aless accurate level is yet configured with the aim of promoting fastswitching from the ready mode into the active mode.

As a further option, which is particularly advantageous in connectionwith an eye tracker that utilizes active illumination, the operation ofthe imaging device in ready mode may include reducing an illuminationintensity of the light source from the value it has in active mode. Theillumination may even be dispensed with altogether, by turning the lightsource off, wherein the camera may optionally operate with longerexposure duration and/or pixel binning, so that the imaging device stillprovides output data although at a relatively lower quality. While theillumination is turned off, the duties normally fulfilled by the cameramay alternatively be carried out by a camera for non-visible light, suchas a camera sensitive to infrared radiation in or around the wavelengthrange corresponding to human body temperature.

The personal computer system may include a viewer presence detector,which is adapted to produce a positive and/or a negative detectionsignal causing the imaging device to transfer between modes accordingly.The presence detector may be a proximity detector or motion detectoroperating on the basis of, e.g., optic, acoustic, electromagnetic orcapacitive measurements. It is noted that the presence detection mayrelate either to proximity of a viewer's eye to the imaging device or toproximity of the viewer's face, head or body to the imaging device orthe personal computer system.

It is particularly advantageous to embody the viewer presence detectoras a sensor arranged to detect proximity of a viewer's finger (or hand)to a button, scroll wheel or other hardware that is typically used forinputting data during a work session. The proximity sensor may forexample be mounted in a push button acting as a dedicated input means inthe sense above, notably for entering activation clicks with referenceto a visible item appearing at the gaze position on a display. Such anactivation click may cause activation of the item in the same manner asa conventional mouse click does. When the viewer has been detected inthe above manner as being present, it is ensured that the imaging deviceenters ready mode, so that a switching to active mode, in case work isresumed, can be performed in very short time. The switching time may befurther reduced if this embodiment is used in conjunction with otherfeatures of this invention, such as by using a direct interrupt to carryout this mode switching.

Alternatively or additionally, the personal computer may include anidentifying means for determining the identity of a current viewer. Theidentification may be carried out with reference to a set of predefinedpersonal profiles, wherein each is associated with personalized activemodes including, e.g., values of parameters relevant to eye-trackingand/or energy management. The values may be pre-set by the viewer or bya system administrator with reference to an existing person.Alternatively, they may be generic in nature and pre-stored by a systemdesigner to suit different categories of users.

As a further development of the preceding embodiment, the identifyingmeans is an imaging device which is capable of sensing a viewer's (or inparticular, an identified viewer's) actual viewing condition. By anactual viewing condition is understood the presence of viewing aids,such as eyeglasses or contact lenses, or the wearing of certaingarments, such as a cap or a veil, which information may improve orrender more economical the acquiring and/or computational processing ofeye-tracking data. Such adaptations may include modifying eyeillumination, controlling optical filtering or compensating reflectionsand/or geometrical deformations produced by refractive elements inproximity of the eye. The adaptations may advantageously be encoded asone or more sub-profiles associated with the personalized profilesdiscussed above. For instance, the active mode of the imaging device maybe differentiated into active modes for persons A, B, C, etc., whereinthe active modes for person A may be further subdivided intosub-profiles “person A without eyeglasses”, “person A wearing cleareyeglasses” and “person A wearing sunglasses”.

In a second and third aspect, the invention provides a method foroperating a personal computer system including eye-trackingfunctionalities as well as a computer program product for performing themethod by means of a programmable processor communicatively connectedto—or constituting—said personal computer system. The above featureswhich have been outlined within the first aspect readily carry over tothe second and third aspect, in which they may be used to advantage.

It is noted that the invention relates to all combinations of features,even if they are recited in mutually different claims.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example and not limitation, embodiments of the invention willnow be described with reference to the accompanying drawings, on which:

FIG. 1 illustrates an active, ready and idle mode of an eye-trackingequipment and transitions between these;

FIG. 2 illustrates a further development of the setup in FIG. 1, whereinthe active mode is differentiated into personalized modes; and

FIG. 3 is a generalized block diagram of a personal computer system inaccordance with an embodiment of the invention.

All the figures are schematic and generally only show parts which arenecessary in order to elucidate the invention, whereas other parts maybe omitted or merely suggested.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 schematically shows an active mode A, a ready mode R and an idlemode I of a imaging device in an eye tracker. As outlined above, the eyetracker performs computations of a recursive nature or uses historicdata, so that, on the one hand, a given computing or measuring task maybe facilitated or expedited by results or intermediate results fromprevious computations and measurements and, on the other hand, the eyetracker has considerable wake-up time before it provides accurate andcomplete output data. No result history is maintained in the idle mode,whereas a full result history allowing the eye tracker to take fulladvantage of the previous computations and measurements—is maintained inthe active mode. The full result history may refer to a moving timewindow of values, whereby the least recent values are discarded as newones are entered. The ready mode is characterized by producing andmaintaining a partial result history (e.g., lower sample rate, fewersamples or samples acquired at lower resolution or lower accuracy),representing a trade-off between low energy consumption and highresponsiveness (quantified as, e.g., a short wake-up time). Likewise, inimplementations where various hardware components are associated with awarm-up or initialization time until the component is in a fullyoperational state, the ready mode may correspond to a partiallyoperational mode, wherein not all components operate at full powerand/or some components are completely disabled. Preferably, the disabledcomponents are those which contribute most significantly to the totalpower consumption and/or have the shortest initialization time FIG. 3shows a personal computer system 300, which includes a visual display310 for displaying output data. The visual display 310 may produce animage acting as a reference for gaze-point detection in a HMI includinggaze-based communication; in this case, the gaze point may be determinedby intersecting the detected optic axis of an eye with the image planeof the display 310 and correcting for the off-axis position of the foveain the retina using per se known techniques for this. The personalcomputer system 300 further comprises an imaging device 320, which inthis embodiment comprises one camera 321 and one pulsed light source 322synchronized with the camera 321. Depending on the intended useconditions, alternative embodiment the imaging device 320 may includemore than one camera and more than one light source, but may as welllack a light source altogether. The momentary power of both the cameraand the light source varies with operational parameters such as thesampling and illumination pulse frequency, the intensity and solid angleof illumination, the image resolution and image size, so that apower-saving mode, in particular a ready mode or idle mode, may beachieved by modifying one or more of these parameters. The display 310and the imaging device 320 may be separate free-standing devices asshown on the drawing, or may form one multi-purpose unit. Alternatively,either or both may be embodied as head-mounted devices; this isparticularly advantageous in connection with a hands-free HMI of thetype outlined above.

The personal computer system 300 further comprises input means 330including a dedicated input means 331 (symbolically shown as an “off”button) for entering eye-tracking control data and a general-purposeinput means 332 (symbolically shown as a mouse). Further, the system 300includes a presence sensor 340 (shown as an optical sensor) for sensingthe presence of a viewer or, possibly, a viewer's eye, as well as anidentifying means 350, such as a biometric sensor (shown as a linescanner for fingerprints). In the figure, the peripherals discussed sofar are shown connected to a central unit 360, possibly including aprocessor (not shown), and may be embodied as physically separatecomponents or as integral parts of the central unit 360. In thisembodiment, the imaging device 320 supplies its output data to thecentral unit 360, which is responsible for executing a program (e.g., adesktop environment or application software) providing a user interfacewith which the user interacts. In portable computers and smart phones,the peripherals are commonly embodied within a common housing.

The configuration that FIG. 3 illustrates relates to a solution with arelatively low degree of hardware integration. A possible alternativehereto may be obtained by utilizing the camera 321 as a presence sensor,so that no dedicated component is required to detect user presence. Thismay be achieved with negligible inconvenience, since presence detectionis most relevant in the idle or ready mode, when the camera 321 istypically operated at reduced frame rate and/or resolution. Also, theidentifying means 350 may be integrated in the imaging device 320, e.g.,in the form of face recognition iris recognition identifying means.

Further, the viewer presence detector may be embodied as a proximitysensor arranged in a touch input device, such as the mouse 332 or thebutton 331 in FIG. 3. This makes it possible to predict input of newdata and put the eye tracker 320 in ready mode so as to let the delay,which is associated with this mode change, elapse at an earlier pointthan after the first input data arrive.

It will be appreciated that further integration of several functionsinto one hardware unit is possible, as is distribution of onefunctionality over several collaborating hardware units.

As shown in FIG. 1, transitions from any mode to any other mode areenabled. In this embodiment, the mode transitions are triggered bysignals provided by the presence sensor 340, a “off” button 331 forentering eye-tracking control data (forcing of the eye-trackingequipment into idle mode) and general-purpose input means 332 forentering input data other than eye-tracking data and eye-trackingcontrol data. The switching between modes may proceed as indicated inTable 2.

TABLE 2 Mode transitions From/ To Trigger condition S1 R→A Thegeneral-purpose input means 332 receive data. S2 A→R The general-purposeinput means 332 have not been used for a first predetermined timeinterval. S3 I→R The presence sensor 340 detects that a viewer ispresent. Alternative trigger: the imaging device 320 in low-power modedetects that a viewer is present and his or her approximate gazedirection is at the visual display (wake on gaze). The approximatedetection may for instance be configured to detect two pupils that areseen in a direction close to the frontal direction, that is, wherein thepupils are moderately elliptic and do not differ above a given thresholdfrom a circular shape. S4 R→I The presence sensor 340 detects that noviewer is present. Alternative trigger: the presence sensor 340 has notdetected presence of a viewer for a second predetermined time interval.S5 I→A The general-purpose input means 332 receive data. Alternativetrigger: wake on gaze, as detailed above, optionally supplemented byrequiring that a dedicated input means receive data. S6 A→I The presencesensor 340 detects that no viewer is present; alternatively, thepresence sensor 340 has not detected presence of a viewer for a secondpredetermined time interval. S7 A→I The “off’ button 331 is activated.This embodiment achieves an object of the invention since transition S1,the resulting wake-up time of the system, requires less time thantransition S5.

The exemplifying embodiment shown in FIG. 3 lacks a positive dedicatedinput means. It will be appreciated that such positive dedicated inputmeans may be readily included, for instance, as a hardware button forinputting eye-tracking control data. The eye-tracking control data maybe input by depressing the hardware button. As explained earlier, thepressing functionality of the button may alternatively be reserved forinput of other input data that are not related to eye tracking, whereinthe eye-tracking control data are entered by a proximity sensor arrangedwithin the button.

Clearly, such positive dedicated input means may in some embodimentsreplace the “off” button 331 shown in FIG. 3.

Turning to FIG. 2, it will not be discussed how the above setup can befurther developed by differentiating the active mode A into a set ofpersonalized active sub-modes A.1, A.2, A.3, each associated with aknown viewer. This embodiment includes an initial identification step,wherein the viewer is identified using the identifying means 350 and theresult is cached for the duration of a work session. Each transition S1,S5 into the active mode A, whether from the ready mode R or the idlemode I, will then be replaced by a transition into the personalizedsub-mode associated with the identified viewer, in accordance with thecached identification result. Similarly, each transition S2, S6, S7 froma personalized sub-mode into either the ready mode R or the idle mode Imay be carried out substantially as if it happened from the active modeA.

Optionally, the personal profiles may be further refined intosub-profiles A. A.1.b reflecting different viewing conditions, e.g.,wearing of eyeglasses, as described above. Each actual viewing can beobserved optically. By using for instance the presence detector 340 orthe camera 321, the actual viewing condition may be continuouslymonitored for a change in sub-profile, allowing the settings in theactive sub-mode to be adjusted accordingly.

The algorithms illustrated by FIGS. 1 and 2 may be embodied ascomputer-executable instructions distributed and used in the form of acomputer-program product including a computer-readable medium storingsuch instructions. By way of example, computer-readable media maycomprise computer storage media and communication media. As is wellknown to a person skilled in the art, computer storage media includesboth volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage of information suchas computer readable instructions, data structures, program modules orother data. Computer storage media includes, but is not limited to, RAM,ROM, EEPROM, flash memory or other memory technology, CD-ROM, digitalversatile disks (DVD) or other optical disk storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices.Further, it is known to the skilled person that communication mediatypically embodies computer readable instructions, data structures,program modules or other data in a modulated data signal such as acarrier wave or other transport mechanism and includes any informationdelivery media.

1. An imaging device adapted to provide data measurements by imaging atleast one eye of a viewer, wherein: the data measurements describe oneor more of eye position or eye orientation; the imaging device isswitchable between at least an active mode and a ready mode; the imagingdevice is configured, in the active mode, to maintain a first resulthistory of the data measurements based on data gathered based on firstcriteria, the first criteria including a first frame rate; the imagingdevice is configured, in the ready mode, to maintain a second resulthistory of the data measurements based on data gathered based on secondcriteria, the second criteria including a second frame rate that islower than the first frame rate; and upon switching to the active modefrom the ready mode, the imaging device provides additional data basedon a combination of the data measurements from the first result historyand the data measurements from the second result history.